Rankine cycle waste heat recovery system and method with improved EGR temperature control

ABSTRACT

A waste heat recovery (WHR) system and method for regulating exhaust gas recirculation (EGR) cooling is described. More particularly, a Rankine cycle WHR system and method is described, including an arrangement to improve the precision of EGR cooling for engine efficiency improvement and thermal management.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to U.S. Provisional Patent Application No. 61/434,532, filed on Jan. 20, 2011, which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

This disclosure relates to a waste heat recovery (WHR) system and method for regulating exhaust gas recirculation (EGR) cooling and thus temperature control, and more particularly, to a Rankine cycle WHR system and method, including an arrangement to improve the precision of EGR cooling for engine efficiency improvement and thermal management.

BACKGROUND

Increasing the efficiency of internal combustion engines is critical to meet customer expectations and an array of government-mandated regulations. Internal combustion engines generate significant amounts of heat that heat exchangers eventually transfer to the air surrounding the internal combustion engine. Waste heat recovery systems use some of this significant source of heat to improve the efficiency of an internal combustion engine. Waste heat recovery systems may offer additional benefit to an engine beyond converting waste heat to energy or work.

SUMMARY

This disclosure provides an internal combustion engine comprising an exhaust gas recirculation (EGR) system containing an EGR gas and a waste heat recovery (WHR) system adapted to provide cooling to the EGR gas. The WHR system includes a WHR circuit, a fluid containment portion, a feed pump, at least one heat exchanger, an energy conversion portion, and an EGR temperature control circuit connected to the WHR circuit. The feed pump is operable to pump a working fluid from the containment portion through the WHR circuit. The at least one heat exchanger is positioned downstream from the feed pump and is operable to convert the working fluid from a liquid to a high-pressure vapor by transferring heat from the EGR gas to the working fluid. The energy conversion portion is positioned between the heat exchanger and the containment portion. A thermal control unit is positioned along the EGR temperature control circuit to cool the EGR gas and a pressure reduction device is positioned along the EGR temperature control circuit upstream of the thermal control unit to reduce the pressure of the working fluid sufficient to create a phase change of the working fluid.

This disclosure also provides an internal combustion engine comprising an EGR system containing an EGR gas and a WHR system. The EGR system includes at least one heat exchanger and a thermal control unit positioned downstream from the at least one heat exchanger. The WHR system is adapted to provide a working fluid from a containment portion into a WHR circuit and a parallel EGR temperature control circuit. The WHR circuit includes a feed pump, the at least one heat exchanger, and an energy conversion portion. The at least one heat exchanger is adapted to provide cooling to the EGR gas and to change the phase of the working fluid from a liquid to a high-pressure vapor. The EGR temperature control circuit includes the thermal control unit and the thermal control unit is positioned along the EGR temperature control circuit to cool the EGR gas.

This disclosure also provides an internal combustion engine comprising an EGR system containing an EGR gas, a WHR system, at least one sensor and a control system. The EGR system includes at least one heat exchanger and a thermal control unit positioned downstream from the at least one heat exchanger. The WHR system is adapted to provide cooling to the EGR gas. The WHR system includes a WHR circuit, a fluid containment portion, a feed pump, the at least one heat exchanger, an energy conversion portion, a thermal control unit, and a compressor. The feed pump is operable to pump a working fluid from the containment portion through the WHR circuit. The at least one heat exchanger is positioned downstream from the feed pump and is operable to convert the working fluid from a liquid to a high-pressure vapor by transferring heat from the EGR gas to the working fluid. The energy conversion portion is positioned between the at least one heat exchanger and the containment portion. The thermal control unit is connected to the WHR circuit and is positioned along the EGR temperature control circuit to cool the EGR gas. The compressor is positioned along the EGR temperature control circuit to pump working fluid from the thermal control unit. The at least one sensor is positioned along at least one of the EGR system and the WHR circuit. The at least one sensor is adapted to generate an output signal. The control system is adapted to receive the output signal and to generate a control signal based on the output signal to control the speed of at least one of the feed pump and the compressor.

Advantages and features of the embodiments of this disclosure will become more apparent from the following detailed description of exemplary embodiments when viewed in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a conventional internal combustion engine incorporating an exhaust gas recirculation (EGR) system.

FIG. 2 is a schematic of an exemplary embodiment of the present disclosure.

DETAILED DESCRIPTION

Referring to FIG. 1, shown therein is a conventional internal combustion engine 10. Engine 10 may include an engine body or block 12, an engine cooling circuit 14, an air intake system 16, an exhaust system 18, an EGR system 20, and a refrigeration circuit 22.

Engine body or block 12 may include an intake manifold 24 and an exhaust manifold 26. Engine body 12 provides an engine output 28, which may be a shaft or other mechanism (not shown) that drives a vehicle, generator, or other device that is able to make use of the output of engine body 12.

Engine cooling circuit 14 may include a radiator 30 and a fluid pump 32. Engine cooling circuit 14 extends from engine block 12 to radiator 30 and back to engine block 12. Cooling fluid pump 32 is adapted to circulate a cooling fluid and may be positioned along cooling circuit 14 between radiator 30 and engine body 12 in a location that is downstream from radiator 30. A fan 34 may be positioned adjacent to radiator 30 to provide air for heat removal from radiator 30. A mechanical output of engine block 12 may drive cooling fluid pump 32, which moves cooling fluid through engine cooling circuit 14. Cooling fluid pump 32 pushes cooling fluid downstream into engine block 12. The cooling fluid then flows from engine block 12 to radiator 30, where a cooling mechanism, such as fan 34, reduces the temperature of the cooling fluid. The cooling fluid then flows downstream to pump 32 to complete the circuit.

Air intake system 16 extends from an air source 44 to intake manifold 24 and may include a turbocharger 36, a charge air cooler 38, and an EGR mixer 40. Turbocharger 36 includes a compressor 42. Charge air cooler 38 is positioned along air intake system 16 downstream from compressor 42. Between charge air cooler 38 and intake manifold 24 is EGR mixer 40. The rotation of compressor 42, caused by the action of exhaust system 18, described in more detail hereinbelow, compresses air from air source 44. The action of compressor 42 heats the air, which may require cooling before entering intake manifold 24. Charge air cooler 38 receives the compressed air and cools it before the compressed air flows downstream to EGR mixer 40. From EGR mixer 40, the compressed air enters intake manifold 24.

Exhaust system 18 may include a turbocharger turbine 46 and an exhaust outlet 48. High-pressure exhaust gas from exhaust manifold 26 flows downstream to enter turbine 46, causing turbine 46 to rotate. The exhaust gas, at reduced pressure after passing through turbine 46, flows to exhaust outlet 48. Exhaust outlet 48 may connect to various conventional elements and systems, such as aftertreatment devices and an exhaust pipe or exhaust stack (not shown). Turbine 46 connects to compressor 42 by way of a connection 50. Thus, the rotation of turbine 46 causes compressor 42 to rotate.

EGR system 20 extends from exhaust manifold 26 to air intake system 16 and may include an EGR cooler 52, an EGR valve 54, an evaporator 56, and EGR mixer 40, previously described. EGR cooler 52 is positioned along EGR system 20 downstream from exhaust manifold 26. Evaporator 56 is positioned along EGR system 20 downstream from EGR cooler 52 and upstream from EGR mixer 40. EGR valve 54 may be positioned between EGR cooler 52 and evaporator 56. High-pressure exhaust gas flows from exhaust manifold 26 to EGR cooler 52, which decreases the temperature of the EGR gas. From EGR cooler 52, the exhaust gas flows downstream to evaporator 56, which is also part of refrigeration circuit 22, as will be described further hereinbelow. Evaporator 56 provides additional cooling to the EGR gas flowing through EGR system 20. The EGR gas then flows downstream to EGR mixer 40, where the EGR gas mixes with air from intake system 16 prior to entry of the air and EGR gas mixture into intake manifold 24.

Refrigeration circuit 22 includes a thermal expansion valve (TXV) 58, evaporator 56, a compressor 60, and a condenser 62. Refrigeration circuit 22 connects evaporator 56 to condenser 62. Positioned along refrigeration circuit 22 is compressor 60, which is between evaporator 56 and condenser 62 and downstream from evaporator 56. Downstream from condenser 62 and upstream from evaporator 56 is valve 58. Compressor 60 serves to pump a refrigerant through refrigeration circuit 22. As refrigerant flows into evaporator 56, the heat from the EGR gas flowing through evaporator 56, described hereinabove, causes the refrigerant to vaporize. The action of compressor 60 causes the vaporized refrigerant to flow downstream to condenser 62, where fan 34 or other cooling mechanisms cool the refrigerant, causing it to condense to form a liquid. The refrigerant then flows back to evaporator 56, regulated by the action of valve 58, thus completing the refrigeration circuit. Compressor 60 may also be regulated to control the rate of refrigerant flow through circuit 22. The benefit of the ability to adjust the temperature of the EGR gas is that increased cooling of EGR gas may lead to lower emissions of NOx from engine 10.

While the conventional system of FIG. 1 works to cool EGR gas, it does so either by adding a dedicated refrigeration circuit 22 to the engine or by using an existing refrigerant system, such as a vehicle's air conditioning refrigerant system. In either case, refrigeration circuit 22 causes a reduction in the efficiency of internal combustion engine 10.

Referring now to FIG. 2, an exemplary embodiment of the present disclosure is described. Elements in the exemplary embodiment having the same number as the convention embodiment described in FIG. 1 work as described hereinabove are discussed again only as necessary for clarity.

The exemplary embodiment is shown in conjunction with an internal combustion engine 110. Internal combustion engine 110 may include engine body or block 12, engine cooling circuit 14, air intake system 16, exhaust system 18, an EGR system 120, a waste heat recovery system (WHR) 63, and a control system 74. Engine body 12, engine cooling circuit 14, air intake system 16, and exhaust system 18 are described hereinabove.

EGR system 120 includes an EGR circuit 121 extending from exhaust manifold 26 to connect to air intake system 16. EGR system 120 may include a superheater 65, a boiler 66, an EGR valve 68, an EGR thermal control unit (TCU) 70, and EGR mixer 40. EGR system 120 terminates at EGR mixer 40, where EGR system 120 interfaces with air intake system 16. Superheater 65 and boiler 66 may be positioned along EGR system 120 between exhaust manifold 26 and EGR mixer 40 to cool the EGR gas as described hereinbelow. While superheater 65 and boiler 66 are shown as two separate heat exchanger units, they may be a single integrated unit with two sections. In another embodiment, only one single heat exchanger may be used. EGR valve 68 and TCU 70 may be positioned along EGR system 120 between boiler 66 and EGR mixer 40 to further selectively and variably cool the EGR gas thereby controlling EGR temperature as described hereinbelow. A temperature sensor 72 may be located along EGR system 120 between TCU 70 and EGR mixer 40.

WHR system 63 may include a WHR circuit 64, a working fluid cooling and containment portion (FCCP) 76, a filter and dryer 78, a feed pump 80, a check valve 82, a recuperator 84, boiler 66, superheater 65, and an energy conversion portion 86. FCCP 76 may include a condenser, a reservoir and a sub-cooler. The functions of these devices may be performed by a single unit or by a combination of separate units.

Positioned along a first fluid path of WHR circuit 64 downstream of FCCP 76 is feed pump 80. Filter and dryer 78 may be positioned along WHR circuit 64 between FCCP 76 and feed pump 80. Positioned along WHR circuit 64 downstream from feed pump 80 are recuperator 84, boiler 66, and superheater 65. Because of the function of recuperator 84, described in more detail hereinbelow, recuperator 84 is located in two places along WHR circuit 64. The first location is between feed pump 80 and boiler 66. The second location is between superheater 65 and FCCP 76. Energy conversion portion 86 is located along WHR circuit 64 downstream from superheater 65 and upstream from recuperator 84. Check valve 82 may be located between feed pump 80 and recuperator 84. A recuperator bypass 92 may provide a path around recuperator 84 that connects feed pump 80 with boiler 66. The structure and function of the recuperator and the recuperator bypass is discussed in detail in U.S. Pat. No. 7,997,076 issued Aug. 16, 2011, the entire contents of which are hereby incorporated by reference. The connection of recuperator 84 to FCCP 76 completes WHR circuit 64.

Energy conversion portion 86 is capable of producing additional work or transferring energy to another device or system. For example, energy conversion portion 86 may be a turbine, piston, scroll, screw, or other type of expander device that moves, e.g., rotates, as a result of expanding working fluid vapor to provide additional work, which can be fed into the engine's driveline, for example, a driveline or engine output 128 of internal combustion engine 110 by way of a coupling mechanism 94, to supplement the engine's power either mechanically or electrically (e.g., by turning a generator), or it can be used to drive a generator and power electrical devices, parasitics or a storage battery (not shown). Alternatively, energy conversion portion 86 can be used to transfer energy from one system to another system (e.g., to transfer heat energy from WHR system 63 to a fluid for a heating system). One type of energy conversion portion 86 is described in more detail in U.S. patent application Ser. No. 13/347,322, filed Jan. 10, 2012, the entire contents of which is hereby incorporated by reference.

WHR system 63 further includes an EGR temperature control circuit 96 positioned along WHR circuit 64 in parallel with feed pump 80, at least one heat exchanger 65/66, and energy conversion portion 86. Specifically, EGR temperature control circuit 96 is connected to WHR circuit 64 at a position downstream from FCCP 76 to thereby receive working fluid from WHR circuit 64, and further connected to WHR circuit 64 upstream of FCCP 76 to return or deliver working fluid to WHR circuit 64 for delivery to FCCP 76 without flowing through feed pump 80, at least one heat exchanger 65/66, and energy conversion portion 86. The connection of circuit 96 to circuit 64 downstream of FCCP 76 may be upstream of feed pump 80, while the upstream connection of circuit 96 to circuit 64 may be along circuit 64 downstream of recuperator 84. WHR system 63 includes a pressure reduction device 90 and may further include a compressor 88 positioned along circuit 96. Pressure reduction device 90 may be a simple orifice or an expansion valve operable to cause a pressure drop in the fluid flow across the orifice or valve sufficient to cause the working fluid to change phase from a liquid to a gas. Pressure reduction device 90 may be positioned along circuit 96 upstream from TCU 70. Compressor 88 may be positioned along circuit 96 downstream from TCU 70 to pull the gaseous working fluid from TCU 70 and direct it into working fluid circuit 64. Instead of compressor 88, circuit 96 may be connected to circuit 64 downstream of feed pump 80 so that higher pressure working fluid in forced into and through circuit 96 and TCU 70. But, in this case, the evaporation temperature of the working fluid would be limited to that associated with the FCCP pressure. Using the compressor allows for an even lower pressure to be drawn in TCU 70, allowing cooling at temperatures below that attained in the FCCP. Thus, as described hereinbelow, at least a portion of the cool working fluid (liquid phase) flowing from FCCP 76 can be selectively and variably directed through TCU 70 and then returned to FCCP 76 to control the temperature of EGR gas in EGR circuit 121 before it mixes with intake air and returns to the engine body 12.

As shown in FIG. 2, an EGR gas under high pressure flows downstream along EGR system 120 to superheater 65 and then to boiler 66. The EGR gas is cooled as it passes through superheater 65 and boiler 66. However, the primary purpose of superheater 65 and boiler 66, which will be described in more detail hereinbelow, is related to the function of WHR system 63 rather than cooling the EGR gas. Thus, cooling of the EGR gas may be insufficient for optimal efficiency and NOx emission control in internal combustion engine 110. TCU 70, which is downstream along EGR system 120 from EGR valve 68 and from boiler 66, provides cooling of EGR gas flow as its only function. Thus, as will be described in more detail hereinbelow, TCU 70 is able to controllably adjust the temperature of the EGR gas independent of the waste heat recovery function of WHR system 63. The EGR gas, now cooled to an optimal temperature by TCU 70, flows to EGR mixer 40, where it joins airflow in air intake system 16.

WHR system 63, containing a working fluid, is a Rankine cycle waste heat recovery system or an organic Rankine cycle system if the working fluid is an organic high molecular mass fluid with a liquid-vapor phase change that is lower than the water-steam phase change. Examples of Rankine cycle working fluids, organic and inorganic, include Genetron® R-245fa from Honeywell, Therminol®, Dowtherm J™ from Dow Chemical Co., Fluorinol® from American Nickeloid, toluene, dodecane, isododecane, methylundecane, neopentane, neopentane, octane, water/methanol mixtures, or steam. While the system described below may be a Rankine cycle or an organic Rankine cycle, it also presents an opportunity with respect to the EGR system.

FCCP 76 may perform multiple functions including a condenser function, a cooling or sub-cooling function, and a receiver or reservoir function. Feed pump 80 pulls liquid working fluid from FCCP 76 through filter dryer 78, which serves to remove contaminants from the liquid working fluid. Feed pump 80 then moves the liquid working fluid downstream along WHR circuit 64 through a check valve 82 that prevents reverse flow of the liquid working fluid. The liquid working fluid may then pass through recuperator 84 to receive a first heat transfer from vaporized working fluid, which is received from energy conversion portion 86. In cases where the liquid working fluid is warm or the vaporized working fluid requires less cooling, recuperator bypass valve 92 may divert some or all liquid working fluid around recuperator 84. Bypass valve 92 may be a proportional valve that permits a portion of the liquid working fluid to bypass recuperator 84. Alternatively, bypass valve 92 may be modulated to open and close to adjust the amount of liquid working fluid entering recuperator 84.

Downstream from recuperator 84 is boiler 66, which transfers heat from EGR gas to the liquid working fluid, which causes the liquid working fluid to boil or vaporize. The liquid working fluid then flows to superheater 65, which increases the heat content of the vaporized working fluid and evaporates any liquid working fluid that remains. The vaporized working fluid is at high pressure, which flows along WHR circuit 64 to energy conversion portion 86, which has been previously described. As the vaporized working fluid passes through energy conversion portion 86, the temperature and pressure of the vaporized working fluid decreases. The vaporized working fluid flows downstream to recuperator 84, where, as previously described, some of the heat energy transfers to the liquid working fluid flowing into recuperator 84 from feed pump 80. The vaporized working fluid then travels to FCCP 76, where the vaporized working fluid is condensed to a liquid, cooled to the extent necessary to maintain the function of WHR system 63, and stored until the liquid working fluid travels through WHR circuit 64 again.

Temperature control circuit 96 forms a fluid branch that operates in parallel to the above-described path. Liquid working fluid flows into temperature control circuit and then vaporizes. The vapor is then moved downstream to FCCP 76 by the action of compressor 88. Thus, if compressor 88 is off, pressure builds in TCU 70 and working fluid does not flow through temperature control circuit 96. When compressor 88 is on, liquid working fluid flows through valve 90, which may be a thermal expansion valve, into TCU 70. Because the EGR gas flow through TCU 70 has a temperature greater than the phase change temperature of the liquid working fluid, TCU 70 functions to reduce the temperature of the EGR gas while vaporizing the liquid working fluid. Compressor 88 then moves the vaporized working fluid back into the flow path that extends from recuperator 84 to FCCP 76.

Control system 74 may include a control module 98 and a wiring harness 100. Control module 98, which may be a single processor, a distributed processor, an electronic equivalent of a processor, or any combination of the aforementioned elements, as well as software, electronic storage, fixed lookup tables and the like, is connected to certain components of internal combustion engine 110 by wire harness 100, though such connection may be by other means, including a wireless system.

Control module 98 may connect to and send control signals to EGR valve 68, FCCP 76, feed pump 80, valve 90, and bypass valve 92. Control module 98 may also connect to and receive signals from engine body 12, temperature sensor 72, a temperature and pressure sensor 102, a temperature sensor 104, a temperature sensor 106, and a NOx sensor 108. Control module 98 may receive signals from other sensors positioned throughout internal combustion engine 110 that serve to adjust the performance of EGR system 120 and WHR circuit 64. Temperature sensor 102 may be positioned along WHR circuit 64 upstream from feed pump 80. Temperature sensor 104 may be positioned along WHR circuit 64 between recuperator 84 and boiler 66. Temperature sensor 106 may be positioned along WHR circuit 64 downstream from energy conversion portion 86. NOx sensor 108 may be positioned along exhaust system 18.

Control system 74 may serve to control EGR system 120 by first receiving signals from engine body 12, temperature sensor 72, and NOx sensor 108. Engine body 12 may indicate a need to change the temperature of the EGR gas flow into engine body 12 based on, for example, a change in engine operating conditions, such as engine load, or a detected or anticipated change in NOx emissions. Control system 74 may respond by increasing or decreasing EGR flow by adjusting EGR valve 68 to open or close, depending on the signal from engine body 12 and the temperature signal from temperature sensor 72. Control system 74 may also adjust the speed of compressor 88 to increase or decrease the flow of working fluid through TCU 70 to adjust the temperature of the EGR gas flowing through TCU 70. While valve 90 may be a fixed orifice, it may also be adjustable so that as compressor 88 operates, the pressure within TCU 70 may be adjusted, which would thus permit cooling of the EGR gas at different temperature levels since the phase-change temperature of the working fluid varies with pressure. By decreasing the compressor flow rate the pressure in TCU 70 is permitted to build, which increases the phase change temperature and provides less cooling for higher EGR temperature. Conversely, increasing the speed of compressor 88 reduces the pressure in TCU 70 and decreases the phase change temperature, which increases cooling of the EGR gas. Valve 90 may also be adjusted to modify the pressure within TCU 70. For example, increased flow through valve 90 may increase pressure in TCU 70, assuming the speed of compressor 88 remains fixed, which increases the phase change temperature and decreases cooling of the EGR gas. Conversely, reducing flow through valve 90 decreases the pressure, which decreases the phase change temperature and increases cooling of the EGR gas.

Control system 74 may use NOx sensor 108 to control the function of temperature control circuit. More specifically, if NOx sensor 108 indicates a rising level of NOx, control system 74 may respond by increasing the flow of working fluid through TCU 70 by increasing the speed of compressor 88 and/or closing valve 90, thus increasing cooling of the EGR gas.

Control system 74 may control other aspects of WHR circuit 64. For example, a signal received from temperature and pressure sensor 102 may indicate that sub-cooling of the liquid working fluid needs modified to increase the cavitation margin of feed pump 80. Control system 74 may send a control signal to FCCP 76 to adjust sub-cooling, or the speed of feed pump 80 may be adjusted. Temperature sensor 104 may send a signal indicating a need for more heating or less heating of the working fluid as it flows through recuperator 84. Control system 74 may then adjust bypass valve 92 to change the amount of heating provided to the working fluid by recuperator 84. Temperature sensor 106 may indicate a need to adjust the superheat temperature of the working fluid, which may be accomplished by adjusting the flow of EGR gas through the EGR circuit, if the engine condition permits such adjustment, or by adjusting the speed of feed pump 80 and bypass valve 92 to increase or decrease heat transferred to the liquid working fluid prior to the liquid working fluid entering boiler 66.

As will be understood from the foregoing description, TCU 70 provides a significant benefit to the function of internal combustion engine 110. The liquid working fluid routed through temperature control circuit 96 proceeds directly from FCCP 76 to TCU 70 and then back to FCCP 76. Thus, the cooling provided to the EGR gas flow by TCU 70 is independent of the working fluid flow through the portion of the WHR system 63 that passes through energy conversion portion 86, which permits more precise cooling of the EGR gas flow. Thus, TCU 70 permits using WHR system 63 for two separate waste heat recovery system functions while permitting both to operate independent of each other, that being the energy recovered from energy conversion portion 86 and the precise temperature control of the EGR gas flow by TCU 70.

While various embodiments of the disclosure have been shown and described, it is understood that these embodiments are not limited thereto. The embodiments may be changed, modified and further applied by those skilled in the art. Therefore, these embodiments are not limited to the detail shown and described previously, but also include all such changes and modifications. 

We claim:
 1. An internal combustion engine, comprising: an exhaust gas recirculation (EGR) system containing an EGR gas; and a waste heat recovery (WHR) system adapted to provide cooling to the EGR gas, the WHR system including a WHR circuit, a fluid containment portion, a feed pump operable to pump a working fluid from the fluid containment portion through the WHR circuit, at least one heat exchanger positioned downstream from the feed pump and operable to convert the working fluid from a liquid to a high-pressure vapor by transferring heat from the EGR gas to the working fluid, an energy conversion portion positioned between the heat exchanger and the fluid containment portion, an EGR temperature control circuit connected to the WHR circuit and positioned to receive the working fluid from the WHR circuit downstream of the fluid containment portion and to return the working fluid to the WHR circuit upstream of the fluid containment portion, a thermal control unit positioned along the EGR temperature control circuit to cool the EGR gas, and a pressure reduction device positioned along the EGR temperature control circuit upstream of the thermal control unit to reduce the pressure of the working fluid sufficient to create a phase change of the working fluid.
 2. The internal combustion engine of claim 1, further including a compressor positioned along the EGR temperature control circuit.
 3. The internal combustion engine of claim 1, wherein the pressure reduction device includes an expansion valve positioned between the thermal control unit and the fluid containment portion.
 4. The internal combustion engine of claim 3, wherein the expansion valve is adjustable.
 5. The internal combustion engine of claim 2, wherein the speed of the compressor is adjustable.
 6. The internal combustion engine of claim 1, further including a recuperator positioned between the feed pump and the at least one heat exchanger.
 7. The internal combustion engine of claim 1, wherein the at least one heat exchanger is a boiler and a superheater.
 8. An internal combustion engine, comprising: an exhaust gas recirculation (EGR) system containing an EGR gas and including at least one heat exchanger and a thermal control unit positioned downstream from the at least one heat exchanger; and a waste heat reduction (WHR) system adapted to provide a working fluid from a fluid containment portion into a WHR circuit and a parallel EGR temperature control circuit positioned to receive the working fluid from the WHR circuit downstream of the fluid containment portion and to return the working fluid to the WHR circuit upstream of the fluid containment portion, the WHR circuit including a feed pump, the at least one heat exchanger, which is adapted to provide cooling to the EGR gas and to change the phase of the working fluid from a liquid to a high-pressure vapor, and an energy conversion portion, and the EGR temperature control circuit including the thermal control unit positioned along the EGR temperature control circuit to cool the EGR gas.
 9. The internal combustion engine of claim 8, wherein the EGR temperature control circuit includes an expansion valve positioned between the thermal control unit and the fluid containment portion.
 10. The internal combustion engine of claim 8, further including a compressor positioned along the EGR temperature control circuit.
 11. The internal combustion engine of claim 9, wherein the expansion valve is adjustable.
 12. The internal combustion engine of claim 10, wherein the speed of the compressor is adjustable.
 13. The internal combustion engine of claim 8, further including a recuperator positioned between the feed pump and the at least one heat exchanger.
 14. The internal combustion engine of claim 13, further including a bypass valve operable to bypass working fluid around the recuperator.
 15. The internal combustion engine of claim 8, wherein the at least one heat exchanger is a boiler and a superheater.
 16. An internal combustion engine, comprising: an exhaust gas recirculation (EGR) system containing an EGR gas and including at least one heat exchanger and a thermal control unit positioned downstream from the at least one heat exchanger; a waste heat reduction (WHR) system adapted to provide cooling to the EGR gas, the WHR system including a WHR circuit, a fluid containment portion, a feed pump operable to pump a working fluid from the fluid containment portion through the WHR circuit, the at least one heat exchanger positioned downstream from the feed pump and operable to convert the working fluid from a liquid to a high-pressure vapor by transferring heat from the EGR gas to the working fluid, an energy conversion portion positioned between the at least one heat exchanger and the fluid containment portion; an EGR temperature control circuit including the thermal control unit positioned to receive the working fluid from the WHR circuit downstream of the fluid containment portion and to return the working fluid to the WHR circuit upstream of the fluid containment portion to cool the EGR gas, and a compressor positioned along the EGR temperature control circuit to pump working fluid from the thermal control unit; at least one sensor positioned along at least one of the EGR system and the WHR circuit, the at least one sensor adapted to generate an output signal; and a control system adapted to receive the output signal and to generate a control signal based on the output signal to control the speed of at least one of the feed pump and the compressor.
 17. The internal combustion engine of claim 16, wherein the at least one sensor is a temperature sensor positioned in the EGR system downstream from the thermal control unit and adapted to provide the temperature of the EGR gas leaving the thermal control unit.
 18. The internal combustion engine of claim 16, further including an EGR valve positioned between the at least one heat exchanger and the thermal control unit, wherein the control system is adapted to adjust the opening or closing of the EGR valve in response to the output signal.
 19. The internal combustion engine of claim 16, wherein the EGR temperature control circuit includes an expansion valve positioned between the thermal control unit and the fluid containment portion.
 20. The internal combustion engine of claim 19, wherein the expansion valve is adjustable. 